The footings for masonry-type structures such as small buildings and residential housing have been conventionally constructed by digging trenches in the soil according to the layout of the structure, forming wood frames for the footing in the trenches, and then pouring concrete into the space defined by the framing so as to form a continuous concrete tooting upon which the structure can be built. The purpose of this type of footing is to achieve two basic objectives: (1) to minimize total settlement of the structure built on the footing; and (2) to minimize differential settlement between different portions of a structure built on the footing. It is well known that since all footings will settle to some degree, an ideal design is one which provides sufficient resistance to deformation, distributes load forces over large soil areas, and permits uniform settlement of the footing.
The shortcoming of conventional cast-in-place concrete footings for supporting buildings and houses is that the footings are designed so as to be extremely rigid in an attempt to provide uniform pressure on the underlying soil. This requires the aforementioned expensive form work, good site access by concrete trucks and related equipment, and a substantial time for proper curing of the poured concrete footings.
In view of the known shortcomings to the traditional cast-in-place concrete footings, the concept of footings constructed of prefabricated segments was introduced in Europe after World War II due to an urgent need for speed and simplicity in the construction of buildings in order to expedite the post-war reconstruction. This type of prefabricated footing proved viable in Europe and during the years since the war has resulted in a number of prefabricated concrete block systems which are widely known both in Europe and in the United States. A common attribute of many of these prefabricated foundation systems is the use of interlocking blocks of relatively great weight which in some cases require special equipment on-site for placement of the blocks into the desired foundation system.
One interesting prefabricated foundation system is described in U.S. Pat. Nos. 4,703,599 and 4,798,036 assigned to the National Concrete Masonry Association. This system is known commercially as the IDR Footer Block System and comprises individual elongated footer blocks with interlocking side surfaces which are placed in side-by-side abutting relationship without the need for form work or concrete between the individual units. Shallow slots are provided in the top of the individual footer blocks so as to provide a nesting place for reinforcement wire which is placed on top of the foundation wall formed by the footer block foundation system. The reinforcement wire (wire trusses or Rebar) is then covered with a mortar leveling bed upon which the first foundation wall concrete masonry block course is placed. The IDR Footer Block System provides a fast and economical foundation system but does not possess the inherent strength of applicant's footer block system described hereinafter since the individual block units are reinforced only at the top surface thereof with the aforementioned wire reinforcement and mortar leveling bed.